New audio formats: 32 bit float (little and big endian).

At least the little endian version seems to be popular these days. It
is only supported by ALSA, however. To check whether a given wave
file employs one of the two SF_FLOAT formats (aka IEEE float) we have
to consult the format code, a 16 bit integer stored at offset 20 of
the wave header which describes the waveform data according to the
table below.

	0x0001 PCM
	0x0003 IEEE float
	0x0006 8-bit ITU-T G.711 A-law
	0x0007 8-bit ITU-T G.711 MU-law
	0xFFFE Determined by SubFormat

Additional checks are added to check_wav_post_select() which make
sure that the format code is either 1 or 3, and that the number is
compatible with the bits per sample value.